Cascaded optical switch comprising at least one gate

ABSTRACT

The invention pertains to a (cascaded) optical switch at least comprising one input path, a number of output paths, one or more switch or splitter stages each comprising one or more optical switches or splitters, and at least one gate for optically disconnecting the output paths from the input path, wherein that gate is located at or near the input path. The cascaded switches according to the present invention are compact exhibit a reduced complexity and an improved insertion loss.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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Reference to a Microfiche Appendix

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to a (cascaded) optical switch at leastcomprising one input path, a number of output paths, one or more(preferably two or more) switch or splitter stages each comprising oneor more optical switches or splitters, and at least one gate foroptically disconnecting at least one of the output paths from the inputpath.

2. Description of the Related Art

Such a cascaded optical switch is known from E. J. Murphy, “Enhancedperformance switch arrays for optical switching networks,” Proceedings8th European Conference on Integrated Optics, Apr. 2-4, 1997, pp.EFD5-1/563-EFD5-4/566. FIG. 3b of this publication shows a strictlynon-blocking 4×4 switch matrix comprising, in its input stage, four 1×4cascaded switches each consisting of an input path, a first stageconsisting of a passive 3 dB splitter, a second stage consisting of two“dump” or signal disconnect switches, a third stage consisting of two1×2 switches, and four output paths.

The dump switch stage makes it possible for any or all of the signalpaths to be optically disconnected from the network of which they are apart. Disconnection of all signals may be necessary, for instance,during rearrangement of the 4×4 switch matrix or for diagnostics.

FIG. 1 of WO 96/08932 shows a tree-structured (i.e., cascaded) 1×8optical switch wherein each output path is allocated a gate forselectively blocking and unblocking said output as a function of thestate of the 1×2 switch nearest to the output. Disconnection of all theoutputs from the input, as required during the above-describedrearrangement, can be achieved by activating all eight gates so as toblock all outputs.

Another example of a cascaded switch is shown in FIG. 1 accompanyingthis patent application. This cascaded switch comprises one input path(4), a first switch stage (1) consisting of one thermo-optical 1×2switch (viz. a y-junction switch provided with two heater elements), asecond switch stage (2) consisting of two thermo-optical 1×2 switches(the first and second stages forming a 1×4 switch), a third stage (3)consisting of four gates (6; in this case thermo-optical 2×1 switches),and four output paths (5/5′). Again, optical disconnection of all theoutputs from the input can only be achieved by activating all four gatesso as to block all outputs.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to reduce the number of gatesand the power consumption of cascaded switches as described in the firstparagraph. This object is achieved by locating the gate at or near theinput path of the (cascaded) switch, which gate is integrated in aswitch in the stage nearest to the input path and is suitable tooptically disconnect the input path from the output paths of the switchand/or serves to optically disconnect the input path from (all) theoutput paths of the switch.

Thus, the need for a gate at each output path no longer exists and,e.g., in a 1×N cascaded switch the reduction of the number of gatesamounts to ((N−1/N)), which means a reduction of 87.5% for a 1×8cascaded switch. Also, the reduction in power consumption and thereduction of the number of electrical contacts needed to drive thecascaded switch are commensurate with the reduction of the number ofgates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art cascaded switch; and

FIG. 2 illustrates a preferred example of an embodiment of the presentinvention in which the gate is integrated in a switch in the stagenearest the input path.

DETAILED DESCRIPTION

By doing so, the length of the cascaded switch is reduced considerablywithout reducing the effectivity of the blocking action. Moreimportantly, however, the insertion loss of the cascaded switch is, insome instances, reduced by 40% or more. Alternatively, this reduction inlength provides can be used for the addition of further elements (e.g.,means for suppressing crosstalk).

A very effective way of achieving said integration is by way of anembodiment wherein the optical switch or switches in the stage nearestto the input path are 1×(P+1) switches, whereas the optical switches orsplitters in the remaining stages are 1×P switches or 1×P splitters. Oneof the (P+1) outputs of the switch or switches in the stage nearest tothe input path in these instances serves as the gate. This morecompressed design provides devices with a higher density (more input andoutput ports per cm²) and, due to the reduced length of the device,results in a still further reduction of the insertion loss. Furthermore,the number of driving means (viz., heating elements for thermo-opticalswitches and electrodes for electro-optical switches) is further reducedin this design. Preferably P equals 2 or 3, because, in that case,existing and proven elements can be used, which improves reliability andreduces costs.

A preferred example of such an embodiment is shown in FIG. 2. The firstswitch stage (1) consists of a 1×3 switch comprising a gate (7)terminating next to the output paths (5) of the cascaded switch, whilethe second switch stage (2) consists of two 1×2 switches (each connectedto one of the actual outputs of the 1×3 switch), thus forming a 1×4optical switch. Comparison with the 1×4 switch according to FIG. 1clearly shows that the invention (FIG. 2) enables a considerablereduction in length, area, and of the number of switches (3 instead of7). The insertion loss was reduced from 3,5 dB to 2,5 dB, i.e., byapproximately 30%.

By using an absorber in conjunction with the gate, the power in the gateis transformed into a form of energy (for instance, heat) which can haveno detrimental consequences for the functioning of the cascaded switchor the network in which it is integrated. The absorber can, e.g., bemade of a metal. Alternatively, the power in the gate is coupled intothe substrate on which the switch is built.

Also, the gates can be used to monitor the presence of a signal in theinput path of the optical switch or, indeed, for still other functions.

The invention further pertains to an N×M optical switch matrixcomprising at least one cascaded optical switch as described above (withN and M being independent integers, in some cases N equals M).

As explained above, disconnection of all signals may be necessary, forinstance, during rearrangement of the N×M switch matrix. Additionally,each of the cascaded switches comprised in the N×M switch matrixaccording to the present invention through which no signal propagates,can be disconnected individually during normal operation of the N×Mswitch matrix. Thus, the effects of such an unwanted or unselectedsignal on the performance of the entire switch matrix is substantiallyavoided.

Preferably, the switches according to the invention are thermo-opticaldigital switches. Polymers are very suitable for manufacturing suchswitches, since even a modest temperature change can give rise to alarge change in refractive index.

Devices according to the invention can be used with advantage in opticalcommunications networks of various kinds. Generally, the opticalcomponents either will be directly combined with optical components suchas light sources (laser diodes) or detectors, or they will be coupled toinput and output optical fibres, usually glass fibres.

An integrated thermo-optical device may be built up, e.g., as follows.Underneath the waveguiding structure there is a support such as a glassor silicon substrate. On the substrate the following successive layerscan be identified: a lower cladding layer, a core layer (guiding layer),and an upper cladding layer. The cladding material may be glass or apolymeric material. Said cladding layers have an index of refractionlower than that of the core layer. The core layer, which comprises theactual waveguiding channels or paths, may be made of inorganic orpolymeric material.

When using a polymeric core layer, the use of polymeric cladding layersis preferred. In these all-polymeric devices it is easy to adjust thephysical properties of the various layers one to the other, providing amore stable device. The polymers used for these layers are so-calledoptical polymers. For details concerning the theory on which theoperation of thermo-optical switches is based and details about suitablematerials and manufacturing methods reference may be had to WO 96/38756.

As will be clear from the above, the gates primarily serve to opticallydisconnect the input path from the output paths of the cascaded switch.Other suitable terms for gates are, e.g., shutter and idle port(depending, amongst others, on the configuration of thereof). Suitableconfigurations are, e.g., additional branches, cut-off waveguides, andMach-Zehnder interferometers.

The switches comprised in the stages of the (cascaded) switch may, forinstance, be 1×2 or 1×3 DOS switches, 2×2 switches, Mach-Zehnderswitches, or directional coupler switches.

Within the framework of the present invention, the output paths and theinput path are considered optically disconnected when the ratio ofoptical power in the input path over the power in the said output pathis either larger than 15 db or such that the optical power in the outputat hand has dropped below the level required by the system into whichthe switch is integrated.

What is claimed is:
 1. A cascaded optical switch at least comprising oneinput path, a number of output paths, one or more switch or splitterstages each comprising one or more optical switches or splitters, and atleast one gate for optically disconnecting at least one of the outputpaths from the input path, characterized in that the gate is integratedin a switch in the stage nearest to the input path and is suitable forother functions than as a polarization compensator only, said cascadedoptical switch also characterized in that the optical switch or switchesin the stage nearest the input path are 1×(P+1) switches, whereas theoptical switches or splitters in the remaining stages are 1×P switchesor splitters.
 2. A cascaded optical switch according to claim 1, whereinsaid cascaded optical switch is used in an N×M optical switch matrix. 3.A cascaded optical switch, according to claim 1, characterized in that Pequals 2 or
 3. 4. A cascaded optical switch according to claim 3,wherein said cascaded optical switch is used in an N×M optical switchmatrix.
 5. A cascaded optical switch, according to claim 1,characterized in that it comprises two or more switch or splitterstages.
 6. A cascaded optical switch according to claim 5, wherein saidcascaded optical switch is used in an N×M optical switch matrix.
 7. Acascaded optical switch, according to claim 5, characterized in that Pequals 2 or
 3. 8. A cascaded optical switch according to claim 7,wherein said cascaded optical switch is used in an N×M optical switchmatrix.
 9. A cascaded optical switch at least comprising one input path,a number of output paths, one or more switch or splitter stages eachcomprising one or more optical switches or splitters, and at least onegate for optical disconnecting at least one of the output paths from theinput path, characterized in that the gate is integrated in a switch inthe stage nearest to the input path and is suitable to opticallydisconnect the input path from the output paths, said cascaded opticalswitch also characterized in that the optical switch or switches in thestage nearest the input path are 1×(P+1) switches, whereas the opticalswitches or splitters in the remaining stages are 1×P switches orsplitters.
 10. A cascaded optical switch according to claim 9, whereinsaid cascaded optical switch is used in an N×M optical switch matrix.11. A cascaded optical switch, according to claim 9, characterized inthat P equals 2 or
 3. 12. A cascaded optical switch according to claim11, wherein said cascaded optical switch is used in an N×M opticalswitch matrix.
 13. A cascaded optical switch, according to claim 9,characterized in that it comprises two or more switch or splitterstages.
 14. A cascaded optical switch according to claim 13, whereinsaid cascaded optical switch is used in an N×M optical switch matrix.15. A cascaded optical switch, according to claim 13, characterized inthat P equals 2 or
 3. 16. A cascaded optical switch according to claim15, wherein said cascaded optical switch is used in an N×M opticalswitch matrix.